Device to prevent the occurrence of back-firing in mercury arc rectifiers



Feb. 9, 1 932. A. GAUDENZI 1,844,090

DEVICE TO PREVENT THE OCCURRENCE 013 BACK FIRING IN MERCURY ARCRECTIFIERS Filed Aug. 15, 1929 l'fomey Patented Feb. 9, 1932 UiTEl)STATES ARTHUR GAUDENZI, or renew, SWITZERLAND, essrenon 'ronxrinnensnnnsonnnr renown :eovanr & can, or BADEN, swrrznanann, AJOINT-STOCK coiurenv or SWITZERLAND DEVICE TO PREVENT THE OCCURRENCE OFBACK-FIRING IN MERCURY ARC RECTIFIER/S Application filed August 15,1929, Serial No. 386,184, and iniGermany August 16, 1929,

As is already known, the occurence of backfiring in mercury arcrectifiers with glass or metal containers is to some extent prevented bysurrounding the anodes on all sides with sieve patterned anode gridswhich lie in the so-called Hittorfs or Crookes, dark space, i. e., thedark space lying between the anode surface and the negative glow spaceevidenced during periods of negative potential charges of the anode. Thedanger of back-firing is still further reduced by dimmishing the densityof the vapour in the pro);- imity of the anode. For this purpose, as 1salready known, not only the anodes them selves but also the arc guidingshields are heated. Further, it has already been proposed to make thesieve type anode grids surrounding the anodes of a hollow constructionand to cool them in order to prevent the formation of corona spots onthe anode. Such devices, however, have not entirely averted the dangerof back-firing.

According to the invention, the grids of mercury arc rectifiers, inwhich the anodes are each surrounded on all sides within the definedHittorfs dark space by a grid of the sieve pattern, are provided withadditional heating, independent of the rectifier opera tion, in order todiminish the Vapour density in front of the anode. By means of thisheating, which does not reduce the quantity of heat developed duringoperating conditions, the vapour immediately surrounding the anodes isexpanded so that streams of vapour rising from the cathode to the anodeswill be deflected from the anodes. The heating has the furtheradvantage, over the methods already known in which the grids are heatedby the main arc and by radiation from the anodes, that the temperaturein the proximity of the anodes is considerably higher. The heating canbe arranged in a Suitable manner by means of electric current. Any otherdesired means may however be employed. The grid would, for example, bemade hollow to allow the circulation of a gas or a liquid should eitherof these be used; In order to diminish further the vapour density in theneighborhood of the anodes, the anodes themselves may besides be addi-AT n o'rFicE j tionally heated as is already known,by elec v trical orby other means. As is also known the anodes and anode grids are mostsuitably manufactured from an electrically :conduck tive material havinga high v'meltingpoint such. as tungsten, molybdenum etc'., or insteadfrom graphite. 7

Thedrawing -shows an example of the struction of the invention.

It represents a rectifier in section, the left half of the figureillustrating an electrical method of heating the grid and the right halfshowing the hollow construction of the same which allows it to beheated, on the circulation principle, by any desired medium. a is thedouble walled cooled rectifier container of metal having the anodes b, 0which enter the cover but are insulated from it and which are fed fromthe trans former (Z. The cathode is markede. f and f are the anode gridswhich surround the anodes on all sides and which lie within the Hittorfsdark space 9 shown shaded. The

OOl1- source It supplies heating current both to sieve patterned anodegrid f towhich it isconnected as well as to the windingi which serves toheat the anode. The grid f on the other hand is designed in the form ofa hollow heating spiral which allows any desired medium whether liquidor gas to be circulated through it. a i

The invention claimed is:

1. In a mercury arc rectifier. the combina tion with an anode. and agrid surrounding said anode within the Hittorfs dark space, of means forheating the said grid to reduce the vapor density adjacent the saidanode.

2. In a mercury arc rectifier, the combination with ananode subject todestructive e'ffects of excessive vapor pressures, and a sievelike gridwholly surrounding the said grld within the Hittorts dark space, ofmeans for electrically heating the said grid to regrids to reduce thevapor density adjacent the said anodes.

4:. In a mercury arc rectifier comprising a plurality of anodes, a gridsurrounding each of said anodes Within the Hittorfs dark space, meansfor heating each of said anodes to reduce the vapor density adjacentthereto, and means for heating each of said grids to additionally reducethe vapor density adjacent the said anodes.

5. In combination With a mercury arc rectifier comprising a plurality ofanodes subject to injurious effects resulting from excessive Vaporpressures, a grid surrounding each of said anodes Within the Hit-torfsdark space,

means for heating said grids from the said anodes and electricalmeansfor additionally heating said grids to reduce the vapor pressuresadjacent the said anodes.

In testimony whereof I have hereunto subscribed my name this 29th day ofJuly A. D.

. ARTHUR GAUDEYNZI.

